The Dependence of Electrophysiological Derangements on Accumulation of Endogenous Long-Chain Acyl Camitine in Hypoxic Neonatal Rat Myocytes

To determine whether accumulation of long-chain acyl camitine contributes to electrophysiological abnormalities induced by hypoxia, we characterized effects of normoxic and hypoxic perfusion on the subcellular distribution of endogenous long-chain acyl camitine and transmembrane potentials of cultured rat neonatal myocytes. Hypoxia increased long-chain acyl camitine more than 5-fold. Sodium 2-[5-(4-chlorophenyl)-pentyl]-oxirane-2-carboxylate (10 JIM), a camitine acyltransferase inhibitor, precluded accumulation of long-chain acyl camitine induced by hypoxia. Tissue was processed for electron microscopy by a procedure specifically developed for selective extraction of endogenous short-chain and free camitine but retention of endogenous long-chain acyl camitine. In normoxic-perfused cells, long-chain acyl camitine was concentrated in mitochondria and cytoplasmic membranous components. Only small amounts were present in sarcolemma. Hypoxia increased mitochondrial long-chain acyl camitine by 10-fold and sarcolemmal long-chain acyl camitine by 70-fold. After 60 minutes of hypoxia, sarcolemma contained 1.4 X 10 long-chain acyl camitine molecules//un of membrane volume, a value corresponding to approximately 3.5% of total sarcolemmal phospholipid. Hypoxia also significantly decreased maximum diastolic potential, action potential amplitude and maximum upstroke velocity of phase 0. Sodium 2-[5-(4-chlorophenyI)-pentyl]-oxirane-2-carboxylate inhibited accumulation of long-chain acyl camitine in each subcellular compartment and prevented the depression of electrophysiological function induced by hypoxia. These results strongly implicate endogenous long-chain acyl camitine as a mediator of electrophysiological alterations induced by hypoxia. (Circ Res 58: 230-240, 1986)